The present invention pertains in general to an apparatus or circuit for detecting intrusion. The present invention pertains, more particularly, to the signature recognition of intrusion by either passive or active digital techniques. Although the present invention may be practiced in connection with intrusion through any object, it is particularly concerned with the detection of breakage in a glass panel.
U.S. Pat. No. 3,889,250 describes an apparatus for detecting the breakage of glass windows and the like. This patent, in particular, shows a modulation-demodulation technique. In the present invention, on the other hand, there is described a detector which employs digital techniques and which may be used either in a passive system or an active system.
Accordingly, one object of the present invention is to provide an intrusion detection system employing digital detection techniques.
A further object of the present invention is to provide an intrusion detection system particularly adapted for detecting the breakage of glass or the like panels and which system is not susceptible to false alarm conditions.
It has been found that when the transducers are secured to the glass panel with the use of a solid substance such as in epoxy, that heat from the sun may cause tensions in the transducers creating a false alarm condition. It is suspected that as the glass expands, the transducer cannot expand therewith and thus signals are established which give a false indication of intrusion.
Accordingly, another object of the present invention is to provide a special holder for the transducers for urging the transducers against the panel or object and having a lubricant disposed between the panel and the transducer permitting free sliding therebetween in the event that the panel expands for any reason such as when the panel is subjected to heat from the sun.
Still another object of the present invention is to provide circuitry for also sensing a break in the voltage line or other tampering with the detection circuit.